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HARDWARE DESCRIPTION
CHAPTER 5
HARDWARE DESCRIPTION
5.1 INTRODUCTION
This chapter provides an overall general description of the EVB hardware. This description is
supported by a simplified block diagram (Figure 5-1) and a memory map diagram (Figure 5-2).
The EVB schematic diagram, located in Chapter 6, can also be referred to for the following
descriptions.
5.2 GENERAL DESCRIPTION
Overall evaluation/debugging control of the EVB is provided by the monitor BUFFALO program
residing in EPROM (external to the MCU) via terminal intervention. The target system interface
is provided by the MCU and PRU devices. RS-232C terminal/host I/O port interface circuitry
provides communication and data transfer operations between the EVB and external terminal/host
computer devices.
5.2.1
Microcomputer
The M68HC11A1 MCU (U10) operates in the expanded mode of operation. This is accomplished
by +5 Vdc applied to the MCU MODA and MODB pins. The MCU configuration (CONFIG)
register (implemented in EEPROM) is programmed such that the ROMON bit is cleared for EVB
operations. When this bit is cleared, MCU internal ROM is disabled , and that memory space
becomes externally accessed space. This allows the memory at $E000-$FFFF to contain the
monitor BUFFALO program (or user program for emulation) in external EPROM.
The monitor program uses the MCU internal RAM located at $0048-$00FF. The control registers
are located at $1000-$103F.
The EVB allows the user to use all the features of the monitor BUFFALO program, however it
should be noted that the monitor program uses the MCU on-chip RAM locations $0048-$00FF
leaving only 72 bytes for the user (i.e., $0000-$0047). This should be remembered when writing
code.
M68HC11EVB/D
5-1
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